Auto-igniting pyrotechnic booster composition

ABSTRACT

The present invention generally relates to auto-ignition/booster compositions for inflators of occupant restraint systems, for example. An exemplary auto-ignition composition in accordance with the present invention includes a metal chlorate, an auto-ignition fuel selected from the group including sugars and orgainic acids, and a nitrogen-containing secondary fuel.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 60/539,798 filed on Jan. 28, 2004.

BACKGROUND OF THE INVENTION

Auto-ignition materials in automotive air bag inflators allow the deviceto safely deploy in the event of a fire. By including an auto-ignitioncomposition the likelihood of a safety hazard resulting from thebursting of an inflator is substantially reduced.

On the other hand, pyrotechnic booster compositions raise the operatingpressure of a pressure vessel or inflator prior to ignition of the mainor primary gas generant. As a result, ready ignition of the primary gasgenerant is facilitated along with sustained combustion thereof.

Accordingly, most inflators or gas generators for vehicle occupantprotection systems, for example, typically include an auto-ignitioncomposition juxtaposed next to a discrete booster composition. In theevent of a fire, the auto-ignition composition ignites to thereby ignitethe booster composition which thereby ignites the main gas generant. Assuch, the fire hazard is substantially mitigated.

An ongoing challenge is to continue simplification of gas generatormanufacturing processes thereby resulting in lower overall costs. Assuch, combining the auto-ignition and booster compositions into onecomposition would simplify the manufacture and assembly of a gasgenerator, one employed in a vehicle occupant protection system forexample.

SUMMARY

A pyrotechnic formulation including an auto-ignition fuel, anauto-ignition oxidizer, a booster fuel, a booster oxidizer, and anoptional fuel/binder such as silicone that self-ignites at a specificdesign temperature or temperature range. The pyrotechnic also serves asa booster for pyrotechnic gas generators used as automotive gasgenerators or air bag inflators. Accordingly, the present compositionsmay function both as an auto-ignition pyrotechnic and as a boostercharge pyrotechnic thereby eliminating the need for two separatecompositions in the inflator.

Furthermore, the booster composition also propagates ignition of themain gas generation through flame and/or heat propagation. The sequenceof events for the auto-ignition of an inflator includes the ignition ofthe auto-ignition material, which subsequently ignites the boostermaterial, which in turn ignites the main gas generating pyrotechnic.This invention eliminates the need for individual auto-ignition andbooster pyrotechnics, and replaces them with one single pyrotechniccomponent, greatly simplifying the inflator design, and improvinginflator performance.

By integrating the auto-ignition and booster compounds into onecomposition, the single auto-ignition/booster grain can be molded orpressed to fit the desired inflator design. This component would belarger than a single auto-ignition tablet or grain, whereby a greatersurface area facilitates increased heat conduction relative to primarygas generant and relative to the auto-ignition function in case of afire. This single pyrotechnic also enhances the simplicity of theinflator design.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an inflator assembly in accordancewith the present invention; and

FIG. 2 is a schematic view of a gas generating system and a vehicleoccupant restraint system incorporating the composition of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An auto-ignition component of the present invention includes a fuel, anoxidizer and an optional fuel/binder that self-ignites at a specifictemperature. A fuel is preferably selected from sugars such as d-glucoseand organic acids such as tartaric acid at about 15-45 weight percent ofthe composition. Exemplary organic acids include the various enantiomersof tartaric acid, malic acid, succinic acid, diglycolic acid, malonicacid, trans-glutaconic acid, adipic acid, mucic acid,2,2-Bis(hydroxymethyl) propionic acid, citric acid, phenylmalonic acid,and quinic acid. Exemplary enantiomers of this group include D-tartaricacid, DL-tartaric acid, Meso-tartaric acid, D-glutamic acid, andD-quinic acid. The organic acid should preferably have a melting pointranging from about 125 to about 250° C. and pass a heat aging test at107° C. for 400 hours. Typically, the material to be heat aged may besealed in a glass vial and placed in an oven for 400 hours at 107° C.Or, the composition may be included within an inflator, and the inflatormay be placed in an oven at 107° C. for 400 hours. Afterwards, thematerial may be heated, by induction or by heat gun for example, todetermine the auto-ignition temperature of the sample. Or, the inflatormay be heated at a ramp rate of about 14° C. per minute and evaluatedfor the safe deployment thereof. The auto-ignition temperature of thefuel is preferably about 110 to 250° C. as determined by differentialscanning calorimetry/thermogravimetric analysis (DSC/TGA).

An auto-ignition component oxidizer contains a metal chlorate salt atabout 15-80 weight percent of the composition, preferably potassiumchlorate. The metal chlorate salt may be selected from the groupincluding alkali, alkaline earth, and transitional metal chlorates, andmixtures thereof.

A preferred composition includes a fuel/binder formed from silicone at10-35% by weight of the composition. The term “silicone” as used hereinwill be understood in its generic sense. Hawley describes silicone(organosiloxane) as any of a large group of siloxane polymers based on astructure consisting of alternate silicon and oxygen atoms with variousorganic radicals attached to the silicon:

Or, silicone can be more generically represented as shown in Formula 2(but not thereby limited):

Note, “n” in the Formulas indicates a multiple of the polymeric group orportion of the molecule given within the brackets, to include theorganic groups attached to the silicon.

Exemplary silicones include those disclosed in U.S. Pat. Nos. 5,589,662,5,610,444, and 5,700,532, and, in TECHNOLOGY OF POLYMER COMPOUNDS ANDENERGETIC MATERIALS, Fraunhofer-Institut fur Chemische Technologie(ICT), 1990, each reference and document herein incorporated byreference. Silicone may be provided by any known supplier such asShin-Etsu Silicones of America, Inc. of Akron, Ohio. It will beappreciated that curing and addition of the silicone is done inaccordance with manufacturer instructions.

A most preferred composition contains by weight percent of thecomposition silicone at 20%, potassium chlorate at 20%, tartaric acid at20%, and potassium perchlorate at 40%. It is also preferred that theparticle size of the gas generant constituents be milled or sized toabout 25 microns, although particles of other sizes may also beemployed. A ball grinder or vibratory mill such as an M18-5 Swecovibratory mill may be used to mill the constituents.

A booster component of the present invention contains a fuel and anoxidizer. In general, many known gas generant compositions, for usewithin vehicle occupant protection systems for example, may be employedas the booster component of the present compositions. Known gas generantcompositions as described in U.S. Pat. Nos. 5,035,757, 6,210,505,6,287,400, 6,074,502, 5,872,329, 5,756,929, and 5,531,941, allincorporated by reference, exemplify booster gas generants that functionto raise the pressure of an associated pressure vessel in a knownmanner, thereby propagating combustion of a primary gas generant bed.

The booster component fuel may therefore be selected from the group offuels including nitrogen-containing fuels, guanidines, aminoguanidines,tetrazoles, triazoles, metal and nonmetal salts of tetrazoles andtriazoles, and mixtures thereof. The booster component oxidizer maytherefore be selected from metal and nonmetal salts of chlorates,perchlorates, nitrates, nitrites, permanganates, oxides, and mixturesthereof. The metal salts may be selected from alkali, alkaline earth,and transitional metal salts, and mixtures thereof. The booster fuel,including silicone if desired, preferably represents about 0.1-75 weightpercent of the booster component. The booster oxidizer represents 0-60weight percent of the booster component. A preferred booster oxidizer ispotassium perchlorate. It should be noted that the auto-ignitionoxidizer when properly milled and when provided in relatively largeramounts, may provide a sufficient oxygen balance to provide an oxidizingeffect on both the auto-ignition fuel and on the booster fuel. In thatcase, the booster oxidizer is not necessary. It should also be notedthat the weight percents characterized for both the auto-ignition andbooster components are relative to the total composition once both ofthese components are combined.

When formulating the auto-ignition/booster compositions of the presentinvention, each constituent of each component is first granulated ifprovided in solid form. As such, the auto-ignition component may beformed by mixing granulated potassium chlorate with a granulated sugarand/or granulated organic acid. A planetary mixer may be employed toprovide substantially uniform or substantially homogeneous mixtures ofthe various granules. It will be appreciated that tailoring of the burnrates or ballistic properties may be accomplished through iterativelydetermining the desired average granular size for each constituent. Anyother constituents known for their utility in auto-ignition/gas generantcompositions may also be incorporated into the auto-ignition componentin granulated form. As such, ballistic modifiers, coolants, and otheruseful additives could also be provided in known effective amounts or inknown effective weight percents.

The booster component may be formulated in the same way and thereforethe fuel and oxidizer may be granulated and then mixed as describedabove. Again, other constituents known for their utility inauto-ignition/gas generant compositions such as ballistic modifiers andcoolants may also be provided in known effective amounts or in knowneffective weight percents.

Once each component is formulated, the auto-ignition and boostercomponents may be mixed together as dry granulated solids to result insubstantially uniform or homogeneous mixtures. It should be appreciatedthat the constituents of the present compositions may be mixed togetherin one batch rather than mixing together in two separate auto-ignitionand booster batches respectively. The order of addition of eachconstituent to the ongoing mixture is not critical so long as asubstantially uniform mixture results and the appropriate weightpercents of all of the constituents are maintained.

Accordingly, the gas generant constituents may be mixed by knownmethods. Or, in yet another aspect of the invention, the auto-ignitionfuel such as tartaric acid or d-glucose may first be coated withsilicone and then preferably dry mixed with the other auto-ignition andbooster constituents. The silicone may be cured or uncured prior tomixing with other compositional constituents. The resulting homogeneousmixtures are then pressed into tablets or other useful shapes therebyproviding intimate contact with the various constituents. By coating theauto-ignition fuel with silicone, an insulating barrier is thenintegrated within the gas generant composition between the auto-ignitionfuel, and the auto-ignition/oxidizer such as potassium chlorate. Onceauto-ignition of the auto-ignition fuel and auto-ignition oxidizer(potassium chlorate) begins, then combustion of the booster component,or silicone and potassium perchlorate is initiated. The silicone coatingof the auto-ignition fuel inhibits the Mallard or carmelizing reactionof the fuel, glucose for example, whereby more heat is required forauto-ignition of the auto-ignition fuel thereby improving repeatableperformance combustion characteristics. The gas generant constituents ofthe present invention may be supplied by well known suppliers such asAldrich Chemical Company of Milwaukee, Wis.

In yet another aspect of the invention, if uncured silicone is added toa mixture of the dry granulated constituents of both the auto-ignitionand booster components, an extrudable or thixotropic mixture may beproduced. The uncured mixture may then be applied to any desired surfacewithin an associated gas generator within a vehicle occupant protectionsystem, for example, thereby simplifying gas generator manufacture. Theextruded mixture must, however, be applied to a surface that remains inthermodynamic communication with the temperature outside of the pressurevessel or inflator, and, also fluidly or thermodynamically communicateswith the primary gas generant upon auto-ignition of the extrudedmixture.

Typical inflator assembly methods require the formation of anauto-ignition repository within the inflator structure. Auto-ignitiontablets may then be placed within the repository and sealed or enclosedwithin the repository with a taped seal. A booster composition may thenbe placed proximate to the auto-ignition composition therebyfacilitating thermodynamic communication between the two compositionsupon auto-ignition of the auto-ignition composition.

In contrast, extrudable auto-ignition/booster mixtures containinguncured silicone may be applied directly to a desired surface thatinterfaces with the primary gas generant, and then cured thereafter inaccordance with manufacturer instructions. As such, the surface area ofthe auto-ignition composition in contact with the desired surface may beincreased and/or optimized to provide a more effective interface toincrease and/or tailor thermodynamic communication with the primary gasgenerant chamber. When compared to typical inflator assembly, thepresent auto-ignition/booster compositions provide an improved method ofassembly thereby resulting in ease of assembly and reduced manufacturingcosts.

Alternatively, an auto-ignition/booster composition containing curedsilicone will exhibit resilient and compressible characteristics,thereby permitting placement of the composition in any effective areawithin the inflator that will accommodate impingement of thecomposition. Stated another way, a separate repository for theauto-ignition composition need not be provided so long as an area withinthe inflator may be employed to provide an interference fit for thecompressible auto-ignition/booster charge. All other aspects of inflatormanufacture may be accommodated as known in the art.

Compositions formulated in accordance with the present invention mustauto-ignite at about 150 degrees Celsius or less, must function as abooster charge, and must inhibit the production of noxious gases. Inessence, the compositions of the present invention burn relativelyhotter and therefore the gas pressure is increased. Accordingly, lessgas is needed to pressurize the combustion chamber. Unlike certain knownauto-ignition compositions, preferred compositions of the presentinvention also survive standard heat aging testing at 107 degreesCelsius for 400 hours.

As shown in FIG. 1, an inflator incorporating any of the compositionsdescribed above may be incorporated into a gas generating system 200, asexemplified in FIG. 2. At least a portion of a primary gas generant 19is juxtaposed next to composition 17, thereby facilitating thermodynamiccommunication and/or fluid flow between both compositions uponauto-ignition of the composition 17. Gas generating system 200 includesat least one airbag 202 and an airbag inflator 10 coupled to airbag 202so as to enable fluid communication with an interior of the airbag forinflating the airbag in the event of a collision. Examples of inflatorswhich may be incorporated into gas generating system 200 are describedin U.S. Pat. Nos. 6,764,096, 6,659,500, 6,422,601, 6,752,421 and5,806,888, both incorporated herein by reference. The inflator includesan embodiment of composition 17 as described above for use within theinflator. Gas generating system 200 may also be in communication with acrash event sensor 210 including a known crash sensor algorithm thatsignals actuation of airbag system 200 via, for example, activation ofairbag inflator 15 in the event of a collision.

Referring to FIG. 2, gas generating system 200 may also be incorporatedinto a broader, more comprehensive vehicle occupant restraint system 180including additional elements such as a safety belt assembly 150. FIG. 2shows a schematic diagram of one exemplary embodiment of such arestraint system.

Safety belt assembly 150 includes a safety belt housing 152 and a safetybelt 100 in accordance with the present invention extending from housing152. A safety belt retractor mechanism 154 (for example, a spring-loadedmechanism) may be coupled to an end portion 153 of the belt. Inaddition, a safety belt pretensioner 156 may be coupled to beltretractor mechanism 154 to actuate the retractor mechanism in the eventof a collision. Typical seat belt retractor mechanisms which may be usedin conjunction with the safety belt embodiments of the present inventionare described in U.S. Pat. Nos. 5,743,480, 5,553,803, 5,667,161,5,451,008, 4,558,832, and 4,597,546, incorporated herein by reference.Illustrative examples of typical pretensioners with which the safetybelt embodiments of the present invention may be combined are describedin U.S. Pat. Nos. 6,505,790 and 6,419,177, incorporated herein byreference.

Safety belt system 150 may be in communication with a crash event sensor158 (for example, an inertia sensor or an accelerometer) including aknown crash sensor algorithm that signals actuation of belt pretensioner156 via, for example, activation of a pyrotechnic igniter (not shown)incorporated into the pretensioner. U.S. Pat. Nos. 6,505,790 and6,419,177, previously incorporated herein by reference, provideillustrative examples of pretensioners actuated in such a manner. Again,composition 17 may also be employed within a micro gas generator formedin a known manner within pretensioner 156.

It will be understood that the foregoing description of an embodiment ofthe present invention is for illustrative purposes only. As such, thefeatures herein disclosed are susceptible to a number of modificationscommensurate with the abilities of one of ordinary skill in the art,none of which departs from the scope of the present invention as definedin the appended claims.

1. A gas generating system comprising a composition, the compositioncomprising: a metal chlorate; a first fuel selected from the groupconsisting of sugars and organic acids; and a nitrogen-containingsecondary fuel.
 2. The gas generating system of claim 1 wherein saidcomposition comprises silicone as a fuel/binder at about 10-30 weightpercent of the composition.
 3. The gas generating system of claim 1wherein said nitrogen-containing secondary fuel is selected from thegroup consisting of selected from the group consisting of guanidines,aminoguanidines, tetrazoles, triazoles, salts of guanidines, salts ofaminoguanidines, salts of tetrazoles, salts of triazoles,nitrogen-containing fuels, and mixtures thereof.
 4. The gas generatingsystem of claim 1 comprising a secondary oxidizer selected from thegroup consisting of metal and nonmetal perchlorates, oxides, nitrites,nitrates, permanganates, and chlorates provided at about 0.1-60 weightpercent of the total composition.
 5. The gas generating system of claim1 wherein said system is an airbag inflator.
 6. The gas generatingsystem of claim 1 wherein said system is a seatbelt pretensioner.
 7. Thegas generating system of claim 1 wherein said system is a vehicleoccupant protection system.
 8. The gas generating system of claim 1wherein said metal chlorate is provided at about 15-45%, said first fuelis provided at about 15-45%, and said secondary fuel is provided atabout 0.1-70%, said percentages stated by weight of the totalcomposition.
 9. The gas generating system of claim 1 wherein said metalchlorate is selected from the group consisting of alkali, alkalineearth, and transitional metal chlorates.
 10. An auto-ignitioncomposition comprising: a metal chlorate; a first fuel selected from thegroup consisting of sugars and organic acids; and a nitrogen-containingsecondary fuel.
 11. The auto-ignition composition of claim 10 whereinsaid metal chlorate is provided at about 15-45%, said first fuel isprovided at about 15-45%, and said secondary fuel is provided at about0.1-70%, said percentages stated by weight of the total composition. 12.The auto-ignition composition of claim 10 wherein said compositionfurther comprises silicone as a fuel/binder at about 10-30 weightpercent of the composition.
 13. The auto-ignition composition of claim10 wherein said nitrogen-containing secondary fuel is selected from thegroup consisting of selected from the group consisting of guanidines,aminoguanidines, tetrazoles, triazoles, salts of guanidines, salts ofaminoguanidines, salts of tetrazoles, salts of triazoles,nitrogen-containing fuels, and mixtures thereof.
 14. The auto-ignitioncomposition of claim 10 further comprising a secondary oxidizer selectedfrom the group consisting of metal and nonmetal perchlorates, oxides,nitrites, nitrates, permanganates, and chlorates, said secondaryoxidizer provided at about 0.1-60 weight percent of the totalcomposition.
 15. The auto-ignition composition of claim 10 wherein saidmetal chlorate is selected from the group consisting of alkali, alkalineearth, and transitional metal chlorates.